Samsung has 2.8 GHz GDDR4

When Nvidia and ATI gets tired of GDDR3, Samsung will have a nice range of GDDR4 to offer. It starts at modest 1.1GHz or 2.2 GHz effectively, works its way up to 1.2 GHz or 2.4 GHz effectively and then finally stop at 1.4 GHz or 2.8 GHz effectively.

We are almost certain that this memory will be able to overclock up towards 3 GHz or at least close.

It is listed as K4U52324QE and it can provide up to 11.2GB/s per chip.